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A New Fast Motion Estimation Algorithm Based on H.264LI Hong-ye, LIU Ming-jun, ZHANG Zhi-qiangMINES 2009

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Fast and Efficient Fractional Pixel Motion Estimation for H.264/AVC Video CodingHumaira Nisar and Tae-Sun Choi, Senior Member, IEEEICIP 2009

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Outline • Introduction • Introduction to UMHexagonS • New Fast Motion Estimation Algorithm• Simulation• Introduction to Fractional Motion Estimation• Fractional Pixel Error Surface• Quadrant Based Directional Fractional Pixel ME

Algorithm• Simulation• Conclusion

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Introduction • Motion estimation(ME) is time consuming. Many

fast motion estimation algorithms which have been proposed still can’t satisfy the real-time application.

• ME consists of two stages:• Integer pixel ME• Fractional pixel ME

• Generally Integer pixel ME takes most of computational time of the whole ME. Due to the development of fast ME algorithm, computational cost of integer pixel has been greatly reduced.

• Fractional ME has strong impact on PSNR, and has complex sub pel interpolation process.

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Block Matching Algorithm – Full Search

• Integer-pixel• Search range =

• Fractional-pixel• Search range =

16

163

3

=1089

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Introduction to UMHexagonS • Combine many strategies together and achieve

both fast speed and high accuracy. • Performs well both in small motion sequences and

large motion sequences.• Adaptively adopt different searching pattern

according to SAD and have early termination strategy to reduce searching time.

• Only 10% complexity compare with Full Search algorithm.

• Adapted in H.264 reference software.[10] Zhibo Chen, Jianfeng Xu, Yun He, and Junli Zheng, “Fast integer-pel and fractional-pel motion estimation for H.264/AVC,”Journal of Visual Communication & Image Representation, April 2006, pp. 264-290.

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Introduction to UMHexagonS • Search process of

UMHexagonS algorithm, search range = (

0)

(1)

(2)(

3)(4-1)(4-2)

`

Step1: Unsymmetrical-cross searchStep2: Small rectangular full searchStep3: Uneven multi-hexagon-grid search Step4: Extended hexagons-based search

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New Fast Motion Estimation Algorithm• Ameliorates UMHexagonS algorithm to reduce

search point on three aspects:

Proposed algorithm UMHexagonS algorithm

New square pattern Step2: Small rectangular full search

Multi-octagon-gird search Step3: Uneven multi-hexagon-grid search

Add Horizontal and vertical hexagon

Step4: Extended hexagons-based

replace

New Square Pattern

• 5x5 full search 3x3

• By studying the distribution of MV• 80% in 5x5 grid region• 70% in 3x3 grid region

• Replace reason• 80%70%• 5x5=253x3=9 36%

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Multi-Octagon-Grid Search

• Hexagon(6) Octagon(8)

• Replace reason• Octagon has more edges than hexagon and closing to circle• 16 points 8 points 50%

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Horizontal Hexagon and Vertical Hexagon

• Add horizontal and vertical hexagons

• Add reason• Orientation bias

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Uniform Horizontal Vertical

Search pattern Adopt pattern

16x16, 8x8 Uniform hexagon

16x8, 8x4 Horizontal hexagon

8x16, 4x8 Vertical hexagon

4x4 Go to step 4-2

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Simulation

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Introduction to fractional motion estimation

HFPS: 17 points CBFPS

[2] Z. Chen, P. Zhou, Y. He and Y. Chen, “Fast Integer Pel andFractional Pel Motion Estimation for JVT” ITU-T, Doc.#JVT-F-017, Dec. 2002.”

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Fractional Pixel Error SurfaceError surface of fractional-pel

motion estimation (1/8-pel case)

• Unimodal error surface• Redundant to check

opposite direction points

Error surface of integer-pel motion estimation (search range = 32)

• Drop into local minimum

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Quadrant Based Directional Fractional-Pixel ME Algorithm

Condition Quadrant selection Approach

D(X) D(Z) D(X) D(Y)

Quadrant I

D(X) D(Z) D(X) D(Y)

Quadrant II

D(X)D(Z) D(X) D(Y)

Quadrant III

D(X)D(Z) D(X) D(Y)

Quadrant IV

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Quadrant Based Directional Fractional-Pixel ME Algorithm Half pel points:

Step1: Calculate the cost of the best integer-pel position and 2 search points .

Step2: Use quadrant selection approach selects quadrant, and selects additional ½ pel points.

Case1: For quadrant I, only one additional ½ pel point is selected. Case2: For quadrant II, two

additional ½ pel points are selected. Case3: For quadrant III, three

additional ½ pel points are selected. Case4: For quadrant IV, two

additional ½ pel points are selected.

Choose the best ½ pel point for search ¼ pel start point.

I

IIIIIIV

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Quadrant Based Directional Fractional-Pixel ME Algorithm

Quarter pel points: search procedure is the same as

½ pel points. At most : 11 points

I

I

IIIIIIV

II

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Simulation

Codec and Profile

JM-12.2 Main Profile

GOP Structure

IPPP

Reference frame

1

Search Range 16

PC Intel Pentium IV 2.66 GHZ CPU

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Simulation

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Simulation

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Conclusion • New fast motion estimation algorithm based on

H.264 improves on the UMHexagonS in three aspects. Reduce 30%~40% computational complexity of UMHexagonS without accuracy loss. Efficient for real time video coding applications.

• Fast fractional search motion estimation algorithm based on uni-modal error surface assumption divides search range into four quadrants and finds the minimum error points by searching only some points that lie in that quadrant. Reduce computation time and keep almost same performance as CBFPS algorithm.